Bidirectional multiple-port power conversion system and method

ABSTRACT

A bidirectional power conversion system includes three power conversion ports. A first power conversion port includes a power factor correction device and a primary power conversion network. A second power conversion port includes a plurality of switches and a plurality of diodes, wherein an output voltage of the second power conversion port is regulated through adjusting an output voltage of the power factor correction device as well as through adjusting an operating parameter of the primary power conversion network. A third power conversion port includes a first switch network and a power regulator connected in cascade, wherein the first power conversion port, the second power conversion port and the third power conversion port are magnetically coupled to each other through a transformer.

PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No.16/899,456, entitled “Bidirectional Multiple-Port Power ConversionSystem and Method,” and filed on Jun. 11, 2020, now U.S. Pat. No.11,165,338 issued on Nov. 2, 2021, which is a continuation ofInternational Application No. PCT/US2019/039174, entitled “BidirectionalMultiple-Port Power Conversion System and Method,” and filed on Jun. 26,2019, each is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to a bidirectional multiple-port powerconversion system and in particular embodiments to a bidirectionalthree-port power conversion system connected between a single-phase ACpower source and a plurality of batteries.

BACKGROUND

The power electronics industry has experienced rapid growth due tocontinuous improvements in the exponential development of newtechnologies. As the power electronics technologies further advances,on-board battery chargers have become a key element for some new energyapplications. One of the most important new energy applications iselectric vehicles (EV). Different EVs are equipped with differentcapacity and voltage batteries. The EVs need suitable chargers forcharging a variety of batteries.

An on-board battery charger comprises electrical circuits for convertingalternating current (AC) power into direct current (DC) power. Theon-board battery charger may include an AC/DC stage and a DC/DC stage.The inputs of the AC/DC stage are connected to the AC utility line. TheAC/DC stage is employed to convert the AC input voltage from the ACutility line to a suitable DC bus voltage. The AC/DC stage may comprisea variety of electromagnetic interference (EMI) filters, a bridgerectifier formed by four diodes and a power factor correction circuit.

The EMI filter is employed to reduce high frequency noise that may causeinterference with other devices of the on-board battery charger. As aresult of employing the EMI filters, the on-board battery charger maymeet various EMI regulations. The bridge rectifier converts an ACvoltage into a full-wave rectified DC voltage. Such a full-waverectified DC voltage provides a DC input voltage for the power factorcorrection circuit. The power factor correction circuit may beimplemented by a suitable power converter such as a boost converter. Byemploying an appropriate control circuit, the boost converter is capableof shaping the input line current to be sinusoidal and in phase with thesinusoidal input voltage of the AC input source. As a result, the powerfactor of the AC/DC stage may be close to unity as required by a varietyof international standards

The DC/DC stage is connected between the outputs of the AC/DC stage anda plurality of batteries. The DC/DC stage may comprise an isolated DC/DCpower converter having one primary winding, a plurality of secondarywindings and a plurality of rectifiers for converting the DC bus voltageinto a plurality of isolated DC voltages for charging the plurality ofbatteries.

SUMMARY

These problems are generally solved or circumvented and the technicaladvantages are generally achieved by preferred embodiments of thepresent disclosure which provide a power conversion system and methodfor bidirectional power transferring between an AC power source and aplurality of batteries.

In accordance with an embodiment, a power conversion system comprisesthree power conversion ports. A first power conversion port includes apower factor correction device and a primary power conversion network. Asecond power conversion port includes a plurality of switches and aplurality of diodes, an output voltage of the second power conversionport regulated through adjusting an output voltage of the power factorcorrection device as well as through adjusting an operating parameter ofthe primary power conversion network. A third power conversion portincludes a first switch network and a power regulator connected incascade with the first switch network, the first power conversion port,the second power conversion port, and the third power conversion portmagnetically coupled to each other through a transformer.

The power factor correction device is a three-level neutral pointclamped power factor correction converter. The primary power conversionnetwork is a three-level inductor-inductor-capacitor (LLC) converter.The plurality of switches and the plurality of diodes form a firstrectifier and a second rectifier connected in parallel to the firstrectifier, the first switch network is a third rectifier and the powerregulator is a step-down DC/DC converter.

The first rectifier includes a first switch, a second switch connectedin series with the first switch, a third switch and a fourth switchconnected in series with the third switch, wherein a common node of thefirst switch and the second switch is connected to a first terminal of afirst secondary winding of the transformer, and a common node of thethird switch and the fourth switch is connected to a second terminal ofthe first secondary winding of the transformer through a first secondarycapacitor. The second rectifier includes a first diode, a second diodeconnected in series with the first diode, a third diode and a fifthswitch connected in series with the third diode, wherein a common nodeof the first diode and the second diode is connected to a first terminalof a second secondary winding of the transformer, and a common node ofthe third diode and the fifth switch is connected to a second terminalof the second secondary winding of the transformer through a secondsecondary capacitor.

The first rectifier and the second rectifier are configured as a firstvoltage doubler and a second voltage doubler, respectively throughconfiguring the fourth switch and the fifth switch as always-onswitches.

The third rectifier includes a sixth switch, a seventh switch connectedin series with the sixth switch, an eighth switch and a ninth switchconnected in series with the eighth switch, wherein a common node of thesixth switch and the seventh switch is connected to a first terminal ofa third secondary winding of the transformer, and a common node of theeighth switch and the ninth switch is connected to a second terminal ofthe third secondary winding of the transformer through a third secondarycapacitor.

In accordance with another embodiment, a method comprises transferringenergy from an AC power source to a first DC load through a power factorcorrection device, a primary power conversion network and a firstsecondary power conversion network, the first secondary power conversionnetwork being magnetically coupled to the primary power conversionnetwork through a transformer and transferring energy from the AC powersource to a second DC load through the power factor correction device,the primary power conversion network and a second secondary powerconversion network that includes a power regulator, the second secondarypower conversion network being magnetically coupled to the primary powerconversion network through the transformer.

The method further comprises regulating a voltage across the first DCload through adjusting an output voltage of the power factor correctiondevice, and regulating a voltage across the second DC load throughadjusting a duty cycle of the power regulator.

The method further comprises configuring the power regulator to operatein a bypass mode in response to a first system operation condition wherean input voltage of the power regulator is within a first predeterminedrange.

The method further comprises configuring the power regulator to operateas a linear regulator in response to a second system operation conditionwhere an input voltage of the power regulator is within a secondpredetermined range.

The method further comprises configuring the first DC load as a powersource to provide power for at least one of the second DC load and an ACload connected to terminals of the AC power source.

The method further configuring the second secondary power conversionnetwork to operate in a boost converter mode by shorting a secondaryside winding of the transformer through turning on two lower switches ofa third rectifier of the second secondary power conversion network,wherein the third rectifier and the power regulator are connected incascade between the secondary side winding and the second DC load.

In accordance with yet another embodiment, a power conversion systemcomprises a power factor correction device and a power conversionnetwork connected in cascade between an AC power source and a firstwinding of a transformer, a first bridge and a second bridge connectedin parallel, wherein the first bridge is between a second winding of thetransformer and a first DC load, and the second bridge is between athird winding of the transformer and the first DC load, and a thirdbridge and a power regulator connected in cascade between a fourthwinding of the transformer and a second DC load.

An advantage of an embodiment of the present disclosure is achieving abidirectional high-efficiency power conversion system between an ACpower source and a plurality of batteries.

The foregoing has outlined rather broadly the features and the technicaladvantages of the present disclosure in order that the detaileddescription of the disclosure that follows may be better understood.Additional features and advantages of the disclosure will be describedhereinafter which form the subject of the claims of the disclosure. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present disclosure. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the disclosure as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a bidirectional multiple-port power conversion systemin accordance with various embodiments of the present disclosure;

FIG. 2 illustrates a block diagram of the bidirectional multiple-portpower conversion system shown in FIG. 1 after the multiple-port powerconversion system is configured to operate as an AC/DC system inaccordance with various embodiments of the present disclosure;

FIG. 3 illustrates a block diagram of a bidirectional three-port powerconversion system in accordance with various embodiments of the presentdisclosure;

FIG. 4 illustrates a schematic diagram of a first implementation of thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure;

FIG. 5 illustrates a schematic diagram of a second implementation of thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure;

FIG. 6 illustrates a schematic diagram of a third implementation of thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure;

FIG. 7 illustrates a block diagram of the bidirectional three-port powerconversion system shown in FIG. 3 after the first DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for the second DC load in accordance withvarious embodiments of the present disclosure;

FIG. 8 illustrates a block diagram of the bidirectional three-port powerconversion system shown in FIG. 3 after the first DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for an AC load in accordance with variousembodiments of the present disclosure;

FIG. 9 illustrates a block diagram of the bidirectional three-port powerconversion system shown in FIG. 3 after the first DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for the second DC load and an AC load inaccordance with various embodiments of the present disclosure;

FIG. 10 illustrates a block diagram of the bidirectional three-portpower conversion system shown in FIG. 3 after the second DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for the first DC load in accordance withvarious embodiments of the present disclosure;

FIG. 11 illustrates a block diagram of the bidirectional three-portpower conversion system shown in FIG. 3 after the second DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for an AC load in accordance with variousembodiments of the present disclosure;

FIG. 12 illustrates a block diagram of the bidirectional three-portpower conversion system shown in FIG. 3 after the second DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for both the first DC load and an AC loadin accordance with various embodiments of the present disclosure;

FIG. 13 illustrates a block diagram of the bidirectional three-portpower conversion system after both the first DC load and the second DCload of the bidirectional three-port power conversion system areconfigured as power sources to provide power for an AC load inaccordance with various embodiments of the present disclosure;

FIG. 14 illustrates a flow chart of a method for controlling thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure;

FIG. 15 illustrates a flow chart of another method for controlling thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure; and

FIG. 16 illustrates a flow chart of yet another method for controllingthe bidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The make and use of the presently preferred embodiments are discussed indetail below. It should be appreciated, however, that the presentdisclosure provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to preferredembodiments in a specific context, namely a bidirectional multiple-portpower conversion system. The present disclosure may also be applied,however, to a variety of power conversion systems. Hereinafter, variousembodiments will be explained in detail with reference to theaccompanying drawings.

FIG. 1 illustrates a bidirectional multiple-port power conversion systemin accordance with various embodiments of the present disclosure. Thebidirectional multiple-port power conversion system 100 is connectedbetween an AC element 101 and a plurality of DC elements 122 and 124.Depending on different applications and design needs, the AC element 101can be implemented as either an AC power source or an AC load. Likewise,the plurality of DC elements 122 and 124 can be implemented as either DCloads or DC power sources.

Throughout the description, the AC element 101 may be alternativelyreferred to as an AC power source 101 or an AC load 101 depending ondifferent system configurations. Likewise, each of the plurality of DCelements 122 and 124 may be alternatively referred to as a DC load or aDC power source depending on different system configurations.

In some embodiments, when the bidirectional multiple-port powerconversion system 100 is configured to convert AC power into DC power,the AC element 101 is implemented as an AC power source from a utilitygrid. More particularly, the AC element 101 may be implemented as asingle-phase AC power source. The plurality of DC elements 122 and 124may be a plurality of DC loads such as battery packs, downstream powerconverters and the like. In some embodiments, the DC elements 122 and124 may be batteries of an electric vehicle. The bidirectionalmultiple-port power conversion system 100 shown in FIG. 1 may functionas an electric vehicle charging converter.

In alternative embodiments, when the bidirectional multiple-port powerconversion system 100 is configured to convert DC power into DC powerbetween different DC loads, one of the plurality of DC elements (e.g.,DC element 122) functions as a DC power source, and another DC element(e.g., DC element 124) is configured as a DC load. The DC power sourceis able to provide power for the DC load through the bidirectionalmultiple-port power conversion system 100. It should be noted that theDC power source (e.g., DC element 122) is capable of providing power fora plurality of DC loads (e.g., DC element 124) through the bidirectionalmultiple-port power conversion system 100.

Furthermore, when the bidirectional multiple-port power conversionsystem 100 is configured to convert DC power into AC power, at least oneof the DC elements (e.g., DC element 122) can be implemented as a DCpower source. The AC element 101 is implemented as an AC load. One(e.g., DC element 122) or a combination of the plurality of DC elements(e.g., DC elements 122 and 124) may provide power to the AC load 101.

In some embodiments, the bidirectional multiple-port power conversionsystem 100 may comprise a transformer having a primary winding and aplurality of secondary windings. The bidirectional multiple-port powerconversion system 100 further comprises a power factor correction deviceand a primary power conversion network connected in cascade between theAC element 101 and the primary winding of the transformer. A pluralityof secondary power conversion networks is connected between theplurality of secondary windings and the DC elements respectively. Thedetailed structure of the bidirectional multiple-port power conversionsystem 100 will be described below with respect to FIG. 2 .

In operation, the bidirectional multiple-port power conversion system100 may be configured as an AC/DC power conversion system. The ACelement 101 is a single phase AC power source. The power factorcorrection device is configured such that the power factor of thebidirectional multiple-port power conversion system 100 is adjusted to alevel approximately equal to unity through adjusting the input currentflowing into the power factor correction device. Furthermore, the powerfactor correction device is capable of varying its output voltage in awide range. Such a wide range helps to regulate a main output voltage ofthe bidirectional multiple-port power conversion system 100.

The primary power conversion network may be implemented as a three-levelinductor-inductor-capacitor (LLC) resonant converter. In someembodiments, the three-level LLC resonant converter is able to operateat a switching frequency substantially equal to the resonant frequencyof the three-level LLC resonant converter. As a result of having athree-level LLC resonant converter operating at a switching frequencysubstantially equal to the resonant frequency, the bidirectionalmultiple-port power conversion system 100 is a high efficiency powerconversion system.

The plurality of secondary power conversion networks are implemented assecondary rectifiers, each of which is able to convert an alternatingpolarity waveform received from a secondary winding of the transformerto a single polarity waveform.

In operation, the bidirectional multiple-port power conversion system100 may be configured as a DC/DC power conversion system. The AC element101 is disconnected from the bidirectional multiple-port powerconversion system 100. One of the DC elements (e.g., DC element 122) isconfigured as a DC power source. At least one of the other DC elements(e.g., DC element 124) is configured as a DC load. The DC power source122 is employed to provide power for the DC load 124 through thebidirectional multiple-port power conversion system 100. In particular,the secondary power conversion network connected to the DC power source122 is configured as a full-bridge switching network. The secondarypower conversion network connected to the DC load 124 is configured as asecondary rectifier. The power is transferred from the DC power source122 to the DC load 124 through the full-bridge switching network, thetransformer and the secondary rectifier.

In operation, the bidirectional multiple-port power conversion system100 may be configured as a DC/AC power conversion system. The AC element101 is implemented as an AC load. At least one of the DC elements (e.g.,DC element 122) is configured as a DC power source. The DC power source122 is employed to provide power for the AC load 101 through thebidirectional multiple-port power conversion system 100. In particular,the secondary power conversion network connected to the DC power source122 is configured as a full-bridge switching network. The primary powerconversion network is configured as a rectifier converting analternating polarity waveform received from the primary winding of thetransformer to a single polarity waveform, and establishing a DC voltagebus. The power factor correction device is configured as an inverter toconvert the DC voltage on the DC voltage bus into an AC voltage for theAC load 101.

In operation, the bidirectional multiple-port power conversion system100 may be configured as a hybrid power conversion system. The ACelement 101 is implemented as an AC load. At least one of the DCelements (e.g., DC element 122) is configured as a DC power source, andat least one of the other DC elements (e.g., DC element 124) isconfigured as a DC load. The DC power source 122 is employed to providepower for the AC load 101 and the DC load 124 simultaneously through thebidirectional multiple-port power conversion system 100. In particular,the secondary power conversion network connected to the DC power source122 is configured as a full-bridge switching network. The secondarypower conversion network connected to the DC load 124 is configured as asecondary rectifier. The primary power conversion network is configuredas a rectifier converting an alternating polarity waveform received fromthe primary winding of the transformer to a single polarity waveform,and establishing a DC voltage bus. The power factor correction device isconfigured as an inverter to convert the DC voltage on the DC voltagebus into an AC voltage for the AC load 101.

FIG. 2 illustrates a block diagram of the bidirectional multiple-portpower conversion system shown in FIG. 1 after the multiple-port powerconversion system is configured to operate as an AC/DC system inaccordance with various embodiments of the present disclosure. Thebidirectional multiple-port power conversion system 100 comprises apower factor correction device 102 and a primary power conversionnetwork 104 connected in cascade between the AC element 101 and aprimary winding NP of a transformer 191. The bidirectional multiple-portpower conversion system 100 further comprises a plurality of secondarypower conversion networks 112 and 114. As shown in FIG. 2 , thesecondary power conversion network 112 is connected between thesecondary windings NS11, NS12 and the DC element 122. The secondarypower conversion network 114 is connected between the secondary windingNS2 and the DC element 124.

It should be recognized that while FIG. 2 illustrates the bidirectionalmultiple-port power conversion system 100 with two secondary powerconversion networks, the bidirectional multiple-port power conversionsystem 100 could accommodate any number of secondary power conversionnetworks and their respective DC elements. Each secondary powerconversion network between the secondary power conversion networks 112and 114 may be connected with two secondary windings like the systemconfiguration of the secondary power conversion network 112.Alternatively, each secondary power conversion network between thesecondary power conversion networks 112 and 114 may be connected withone secondary winding like the system configuration of the secondarypower conversion network 114.

In some embodiments, the power factor correction device 102 of thebidirectional multiple-port power conversion system 100 is configuredsuch that the power factor of the bidirectional multiple-port powerconversion system 100 is adjusted to a level approximately equal tounity through adjusting the input current flowing into the power factorcorrection device 102. The power factor correction device 102 may beimplemented as any suitable power factor correction converters such asboost power factor correction rectifiers, Vienna rectifiers and thelike. The detailed schematic diagram of the power factor correctiondevice 102 will be described below with respect to FIG. 4 .

In some embodiments, the primary power conversion network 104 isimplemented as a three-level LLC resonant converter. More particularly,the primary power conversion network 104 comprises the primary sideswitching network of the three-level LLC resonant converter and aresonant tank. In some embodiments, the primary power conversion network104 is configured as an unregulated power converter. The switchingfrequency of the plurality of switches of the primary power conversionnetwork 104 is equal to the resonant frequency of the resonant tank.Alternatively, depending on design needs and different applications, theswitching frequency of the plurality of switches of the three-level LLCresonant converter may vary in a narrow range to help the bidirectionalmultiple-port power conversion system 100 regulate one of the outputvoltages. The detailed schematic diagram of the primary power conversionnetwork 104 will be described below with respect to FIG. 4 .

The transformer 191 provides electrical isolation between the primaryside (side having 102 and 104) and the secondary side (side having 112and 114) of the bidirectional multiple-port power conversion system 100.In accordance with an embodiment, the transformer 191 may be formed of aprimary transformer winding and a plurality of secondary transformerwindings (e.g., windings NS11, NS12 and NS2) as shown in FIG. 2 . Itshould be noted that the transformer illustrated herein and throughoutthe description are merely examples which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. For example, thetransformer 191 may further comprise a variety of bias windings and gatedrive auxiliary windings.

The secondary power conversion network (e.g., secondary power conversionnetwork 112) converts an alternating polarity waveform received from thesecondary winding of the transformer 191 to a single polarity waveform.The secondary power conversion network may be formed of two pairs ofswitching elements such as the n-type metal oxide semiconductor (NMOS)transistors. Alternatively, the secondary power conversion network maybe formed of two pairs of diodes. Furthermore, the secondary powerconversion network may be formed of a combination of switching elementsand diodes. The secondary power conversion network may also be formed byother types of controllable devices such as metal oxide semiconductorfield effect transistor (MOSFET) devices, bipolar junction transistor(BJT) devices, super junction transistor (SJT) devices, insulated gatebipolar transistor (IGBT) devices and the like. The detailed operationand structure of the secondary power conversion network will bediscussed below with respect to FIG. 4 .

It should be noted that three-level LLC resonant converter is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. The primary power conversion network 104 can beimplemented as any suitable isolated converters such as flybackconverters, forward converters, push-pull converters, half-bridgeconverters, full-bridge converters, any combinations thereof and thelike.

FIG. 3 illustrates a block diagram of a bidirectional three-port powerconversion system in accordance with various embodiments of the presentdisclosure. The bidirectional three-port power conversion system 200 issimilar to the bidirectional multiple-port power conversion system 100shown in FIG. 2 except that only two secondary power conversion networksare connected to the transformer 191.

As shown in FIG. 3 , a first port of the bidirectional three-port powerconversion system 200 comprises the power factor correction device 102and the primary power conversion network 104 connected in cascadebetween the AC element 101 and the primary winding NP. A second portcomprises a first secondary power conversion network 112 connectedbetween the secondary windings NS11, NS12, and the DC element 122. Athird port comprises a second secondary power conversion network 114connected between the secondary winding NS2 and the DC element 124. Asshown in FIG. 3 , the second secondary power conversion network 114comprises a first network 141 and a second network 142 connected incascade. In some embodiments, the first network 141 is a rectifier andthe second network 142 is a power regulator for regulating the voltageapplied to the DC element 124.

FIG. 4 illustrates a schematic diagram of a first implementation of thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure. Thebidirectional three-port power conversion system 200 comprises a powerfactor correction device 102, a primary power conversion network 104, atransformer 191, a first secondary power conversion network 112 and asecond secondary power conversion network comprising a first network 141and a power regulator 142. The power factor correction device 102 isimplemented as a neutral-point clamped (NPC) boost power factorcorrection converter. Throughout the description, the power factorcorrection device 102 may be alternatively referred to as an NPC boostpower factor correction converter. The primary power conversion network104 comprises a primary side network of a three-level LLC resonantconverter. Throughout the description, the primary power conversionnetwork 104 may be alternatively referred to as a three-level LLCresonant converter.

The first secondary power conversion network 112 comprises a dioderectifier and a synchronous rectifier. Throughout the description, thesynchronous rectifier may be alternatively referred to as a firstrectifier, and the diode rectifier may be alternatively referred to as asecond rectifier. The first network 141 is implemented as a synchronousrectifier. Throughout the description, the first network 141 may bealternatively referred to as a third rectifier. The second network 142is implemented as a power regulator. Throughout the description, thesecond network 142 may be alternatively referred to as a power regulatoror a secondary regulator.

As shown in FIG. 4 , the inputs of the NPC boost power factor correctionconverter 102 are connected to an AC power source VIN. The NPC boostpower factor correction converter 102 converts an AC input voltage intothree DC voltage buses, namely VB1, VB2 and VB3 as shown in FIG. 4 . Afirst capacitor C1 is connected between voltage buses VB1 and VB3. Asecond capacitor C2 is connected between voltage buses VB3 and VB2. Thefirst capacitor C1 and second capacitor C2 are employed to reduce theripple components and provide steady DC voltages for the three-level LLCresonant converter 104.

As shown in FIG. 4 , the NPC boost power factor correction converter 102comprises an inductor L1, six switches S1-S6 and four diodes D1-D4. Theswitches S1 and S2 are connected in series between the voltage buses VB1and VB2. The switches S3, S4, S5 and S6 are connected in series betweenthe voltage buses VB1 and VB2. A first output terminal of the AC powersource VIN is connected to a common node of switches S1 and S2. Theinductor L1 is connected between a second output terminal of the ACpower source VIN and a common node of switches S4 and S5. The diodes D1and D2 are connected in parallel with switches S1 and S2 respectively.The diodes D3 and D4 are connected in series between a common node ofswitches S3 and S4, and a common node of switches S5 and S6. The commonnode of diodes D3 and D4 is connected to the voltage bus VB3. Theoperating principle of the NPC boost power factor correction converteris well known, and hence is not discussed herein.

The three-level LLC resonant converter 104 is connected between theoutputs of the NPC boost power factor correction converter 102 and aprimary winding NP of the transformer 191. The three-level LLC resonantconverter 104 comprises a switch network and a resonant tank. As shownin FIG. 4 , the switch network, the resonant tank and the primarywinding NP of the transformer 191 are connected in cascade.

The switch network comprises switches S7, S8, S9 and S10 connected inseries between the voltage buses VB1 and VB2. The common node ofswitches S8 and S9 is connected to the common node of the capacitors C1and C2. The common node of switches S7 and S8 is connected to a firstterminal of the transformer 191 through the resonant tank comprising Lrand Cr. The common node of switches S8 and S9 is connected to a secondterminal of the transformer 191.

The resonant tank may be implemented in a variety of ways. For example,the resonant tank comprises a series resonant inductor Lr, a parallelresonant inductor Lm and a series resonant capacitor Cr.

The series resonant inductor and the parallel resonant inductor may beimplemented as external inductors. A person skilled in the art willrecognize that there may be many variations, alternatives andmodifications. For example, the series resonant inductor may beimplemented as a leakage inductance of the transformer 191.

In sum, the resonant tank includes three key resonant elements, namelythe series resonant inductor, the series resonant capacitor and theparallel resonant inductor. Such a configuration is commonly referred toas an LLC resonant converter. According to the operating principle ofLLC resonant converters, at a switching frequency approximately equal tothe resonant frequency of the resonant tank, the resonant tank helps toachieve zero voltage switching for the primary side switching elementsand zero current switching for the secondary side switching elements.

The transformer 191 may be formed of four transformer windings, namely aprimary transformer winding NP and three secondary transformer windingsNS11, NS12 and NS2 as shown in FIG. 4 . A first rectifier comprisingswitches S11-S14 is connected to first secondary winding NS11 through afirst secondary capacitor CS1. A second rectifier comprising switch S24and diodes D21-D23 is connected to second secondary winding NS12 througha second secondary capacitor CS2. The secondary capacitors CS1 and CS2are employed to achieve a voltage doubler function. For example, whenthe switch S24 is configured as an always-on switch, the secondrectifier is configured as a voltage doubler. More particularly, thesecond rectifier charges the secondary capacitor CS2 from the inputvoltage generated by the secondary winding NS12. The input voltage andthe voltage across the secondary capacitor CS2 are added together. As aresult having the input voltage and the voltage across the secondarycapacitor CS2 added together, the output voltage of the second rectifieris about twice the input voltage.

It should be noted when the second rectifier is configured as a voltagedoubler, the first rectifier should be configured as a voltage doublertoo. In other words, the switch S14 is configured as an always-on switchwhen the switch S24 is configured as an always-on switch.

As shown in FIG. 4 , the outputs of the first rectifier and the outputsof the second rectifier are connected in parallel. An output capacitorCol is connected to the outputs of the first rectifier. Theparallel-connected first rectifier and second rectifier are employed toprovide a DC voltage for a first load RL1. In some embodiments, thefirst load RL1 is a main battery of an electric vehicle. The mainbattery may be a lithium-ion polymer battery. The rated voltage of themain battery is about 360 V. The power of the main battery is about 100kW.

In operation, the first load RL1 can be configured as either a DC loador a DC power source. In some embodiments, the power flowing into thefirst load RL1 (RL1 as a DC load) is much higher than the power flowingout of the first load RL1 (RL1 as a DC power source). For example, thepower flowing into the first load RL1 is about 100 kW. The power flowingout of the first load RL1 is about 10 kW.

During the process of having power flowing out of the first load RL1,the first rectifier comprising switches S11-S14 functions a full-bridgecircuit, and the second rectifier comprising diodes D21-D23 and S24 isdisabled. During the process of having power flowing into the first loadRL1, the first rectifier and the second rectifier are connected inparallel to provide power for the first load RL1. As such, the powerrating of the first rectifier may be one ninth of the power rating ofthe second rectifier. For example, the first rectifier may be of a powerrating of 10 kW. The second rectifier may be of a power rating of 90 kW.During the process of having power flowing into the first load RL1, theparallel connected first rectifier and second rectifier can providepower of 100 kW. On the other hand, during the process of having powerflowing out of the first load RL1, the first rectifier is able toprovide power of 10 kW. One advantageous feature of a low-powerrectifier (e.g., the first rectifier) shown in FIG. 4 is transferringpower through two rectifiers unevenly which helps to reduce the powerrating of one rectifier, thereby achieving a cost-effective solution.

A third rectifier comprising switches S31-S34 is connected to the thirdsecondary winding NS2 through a third secondary capacitor CS3. Asdescribed above, the third rectifier can be configured as a voltagedoubler by configuring the switch S34 as an always-on switch.

The power regulator 142 is implemented as a buck DC/DC converter asshown in FIG. 4 . The duty cycle of the buck DC/DC converter can beadjusted so as to regulate the output voltage applied to a second loadRL2. The power regulator 142 comprises switches S41 and S42 connected inseries between the output of the third rectifier and ground. An inductorL2 is connected to a common node of switches S41 and S42. An outputcapacitor Co3 is connected in parallel with the second load RL2. In someembodiments, the second load RL2 is an auxiliary battery of an electricvehicle. The auxiliary battery may be a lithium-ion polymer battery andthe rated voltage of the auxiliary battery is about 12 V.

According to some embodiments, switches S3-S10, S11-S14, S24, S31-S34and S41-S42 shown in FIG. 4 are implemented as MOSFET or MOSFETsconnected in parallel, any combinations thereof and/or the like.According to alternative embodiments, S3-S10, S11-S14, S24, S31-S34 andS41-S42 may be an insulated gate bipolar transistor (IGBT) device.Alternatively, the primary switches can be any controllable switchessuch as integrated gate commutated thyristor (IGCT) devices, gateturn-off thyristor (GTO) devices, silicon controlled rectifier (SCR)devices, junction gate field-effect transistor (JFET) devices, MOScontrolled thyristor (MCT) devices, gallium nitride (GaN) based powerdevices, silicon carbide (SiC) based power devices and/or the like.

It should further be noted that while FIG. 4 illustrates switchesS3-S10, S11-S14, S24, S31-S34 and S41-S42 follow standard switchconfigurations, various embodiments of the present disclosure mayinclude other variations, modifications and alternatives. For example, aseparate capacitor may be connected in parallel with each switch. Such aseparate capacitor helps to better control the timing of the resonantprocess of the LLC resonant converter.

In accordance with an embodiment, the switches S1 and S2 shown in FIG. 4may be an IGBT device. Alternatively, the switching element can be anycontrollable switches such as MOSFET devices, IGCT devices, GTO devices,SCR devices, JFET devices, MCT devices and the like.

It should be noted that when the switches shown in FIG. 4 areimplemented as MOSFET devices, the body diodes of switches can be usedto provide a freewheeling channel. On the other hand, when the switchesare implemented as IGBT devices, a separate freewheeling diode isrequired to be connected in parallel with its corresponding switch.

As shown in FIG. 4 , diodes D1 and D2 are required to provide reverseconducting paths. In other words, diodes D1 and D2 are anti-paralleldiodes. In some embodiments, diodes D1 and D2 are co-packaged with theirrespective IGBT devices. In alternative embodiments, didoes D1 and D2are placed outside their respective IGBT devices.

It should further be noted that while FIG. 4 shows each bidirectionalswitch (e.g., switches S1 and S2) is formed by diodes and IGBT devicesconnected in an anti-parallel arrangement, one of ordinary skill in theart would recognize many variations, alternatives and modifications. Forexample, the bidirectional switch may be implemented by some newsemiconductor switches such as anti-paralleled reverse blocking IGBTsarrangement. The discussion of the IGBT devices herein is applicable toother IGBT devices of this disclosure.

FIG. 5 illustrates a schematic diagram of a second implementation of thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure. Thebidirectional three-port power conversion system 200 shown in FIG. 5 issimilar to that shown in FIG. 4 except that the power regulator 142 isimplemented as a boost DC/DC converter. As shown in FIG. 5 , switchesS51 and S52 are connected in series between the output of the powerregulator 142 and ground. The inductor L2 is connected to the output ofthe first network 141, and a common node of switches S51 and S52.

FIG. 6 illustrates a schematic diagram of a third implementation of thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure. Thebidirectional three-port power conversion system 200 shown in FIG. 6 issimilar to that shown in FIG. 4 except that the power regulator 142 isimplemented as a buck-boost DC/DC converter.

As shown in FIG. 6 , switches S41 and S42 are connected in seriesbetween the output of the first network 141 and ground. Switches S51 andS52 are connected in series between the output of the power regulator142 and ground. The inductor L2 is connected to a common node ofswitches S41 and S42, and a common node of switches S51 and S52.

One advantageous feature of having a buck-boost DC/DC converter shown inFIG. 6 is the bidirectional three-port power conversion system 200 isable to regulate the output voltage applied to the second load RL2 undervarious load conditions. Furthermore, when the second load RL2 isconfigured as a DC power source to provide power for other DC loadsand/or the AC load, the buck-boost DC/DC converter helps to regulate thevoltage across the capacitor Cot over the full battery voltage range ofthe DC power source.

FIG. 7 illustrates a block diagram of the bidirectional three-port powerconversion system shown in FIG. 3 after the first DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for the second DC load in accordance withvarious embodiments of the present disclosure. In some embodiments, theAC power source may be disconnected from the bidirectional three-portpower conversion system 200. The DC element 122 is a battery, which hasbeen fully charged. The DC element 124 is implemented as a DC load.

In response to this system configuration change, the DC element 122 maybe configured as a DC power source. As indicated by the curved arrow702, the power is transferred from the DC power source 122 to the DCload 124 through the secondary power conversion network 112, the firstnetwork 141 and the second network 142. Referring back to FIG. 4 , thefirst rectifier (S11-S14) of the secondary power conversion network 112functions as a full-bridge converter converting the DC voltage into analternating polarity waveform. The alternating polarity waveform is fedinto the first network 141 through the magnetic coupling betweensecondary windings NS11 and NS2. The first network 141 functions as arectifier converting the alternating polarity waveform into a singlepolarity waveform. The single polarity waveform is a DC voltage, whichis applied to the DC load through the power regulator 142.

FIG. 8 illustrates a block diagram of the bidirectional three-port powerconversion system shown in FIG. 3 after the first DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for an AC load in accordance with variousembodiments of the present disclosure. In some embodiments, the AC powersource may be disconnected from the bidirectional three-port powerconversion system 200. The AC element 101 is implemented as an AC load.

In response to this system configuration change, the first DC load 122may be configured as a DC power source. As indicated by the curved arrow802, the power is transferred from the DC power source 122 to the ACload 101 through the secondary power conversion network 112, the primarypower conversion network 104 and the power factor correction device 102.Referring back to FIG. 4 , the first rectifier (S11-S14) of thesecondary power conversion network 112 functions as a full-bridgeconverter converting the DC voltage into an alternating polaritywaveform. The alternating polarity waveform is fed into the primarypower conversion network 104 through the magnetic coupling betweenwindings NS11 and NP. The primary power conversion network 104 functionsas a rectifier converting the alternating polarity waveform into asingle polarity waveform, which is fed into the power factor correctiondevice 102. The power factor correction device 102 is configured as aninverter, through which the single polarity waveform is converted intoan AC waveform, which is applied to the AC load 101.

FIG. 9 illustrates a block diagram of the bidirectional three-port powerconversion system shown in FIG. 3 after the first DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for the second DC load and an AC load inaccordance with various embodiments of the present disclosure. In someembodiments, the AC power source may be disconnected from thebidirectional three-port power conversion system 200. The AC element 101is implemented as an AC load. The DC element 124 is implemented as a DCload.

In response to this system configuration change, the first DC load 122may be configured as a DC power source. As indicated by the curved arrow902, the power is transferred from the DC power source 122 to the ACload 101 through the secondary power conversion network 112, the primarypower conversion network 104 and the power factor correction device 102.At the same time, as indicated by the curved arrow 904, the power istransferred from the DC power source 122 to the DC load 124 through thesecondary power conversion network 112, the first network 141 and thesecond network 142.

Referring back to FIG. 4 , the first rectifier (S11-S14) of thesecondary power conversion network 112 functions as a full-bridgeconverter converting the DC voltage of the DC power source 122 into analternating polarity waveform. The alternating polarity waveform is fedinto the primary power conversion network 104 through the magneticcoupling between NS11 and NP, and fed into the first network 141 throughthe magnetic coupling between NS11 and NS2. The primary power conversionnetwork 104 functions as a rectifier converting the alternating polaritywaveform into a single polarity waveform. The power factor correctiondevice 102 is configured as an inverter, through which the singlepolarity waveform is converted into an AC waveform, which is applied tothe AC load 101. Similarly, the first network 141 functions as arectifier converting the alternating polarity waveform into a singlepolarity waveform. The single polarity waveform is a DC voltage, whichis applied to the DC load through the power regulator 142.

FIG. 10 illustrates a block diagram of the bidirectional three-portpower conversion system shown in FIG. 3 after the second DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for the first DC load in accordance withvarious embodiments of the present disclosure. In some embodiments, theAC power source may be disconnected from the bidirectional three-portpower conversion system 200. The DC element 124 is a battery, which hasbeen fully charged. The DC element 122 is implemented as a DC load.

In response to this system configuration change, the DC element 124 maybe configured as a DC power source. As indicated by the curved arrow1002, the power is transferred from the DC power source 124 to the DCload 122 through the second network 142, the first network 141 and thesecondary power conversion network 112. Referring back to FIG. 4 , thesecond network 142 is configured as a boost DC/DC converter. The firstnetwork 141 functions as a full-bridge converter converting the DCvoltage generated by the boost DC/DC converter into an alternatingpolarity waveform. The alternating polarity waveform is fed into thesecondary power conversion network 112 through the magnetic couplingbetween NS2 and NS11/NS12. The secondary power conversion network 112functions as a rectifier converting the alternating polarity waveforminto a single polarity waveform. The single polarity waveform is a DCvoltage, which is applied to the DC load 122.

FIG. 11 illustrates a block diagram of the bidirectional three-portpower conversion system shown in FIG. 3 after the second DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for an AC load in accordance with variousembodiments of the present disclosure. In some embodiments, the AC powersource may be disconnected from the bidirectional three-port powerconversion system 200. The AC element 101 is implemented as an AC load.

In response to this system configuration change, the DC element 124 maybe configured as a DC power source. As indicated by the curved arrow1102, the power is transferred from the DC power source 124 to the ACload 101 through the second network 142, the first network 141, theprimary power conversion network 104 and the power factor correctiondevice 102. Referring back to FIG. 4 , the second network 142 isconfigured as a boost DC/DC converter. The first network 141 functionsas a full-bridge converter converting the DC voltage generated by theboost DC/DC converter into an alternating polarity waveform. Thealternating polarity waveform is fed into the primary power conversionnetwork 104 through the magnetic coupling between NS2 and NP. Theprimary power conversion network 104 functions as a rectifier convertingthe alternating polarity waveform into a single polarity waveform. Thepower factor correction device 102 is configured as an inverter, throughwhich the single polarity waveform is converted into an AC waveform,which is applied to the AC load 101.

FIG. 12 illustrates a block diagram of the bidirectional three-portpower conversion system shown in FIG. 3 after the second DC load of thebidirectional three-port power conversion system is configured as apower source to provide power for both the first DC load and an AC loadin accordance with various embodiments of the present disclosure. Insome embodiments, the AC power source may be disconnected from thebidirectional three-port power conversion system 200. The AC element 101is implemented as an AC load. The DC element 124 is a battery, which hasbeen fully charged. The DC element 122 is implemented as a DC load.

In response to this system configuration change, the DC element 124 maybe configured as a DC power source. As indicated by the curved arrow1204, the power is transferred from the DC power source 124 to the ACload 101 through the second network 142, the first network 141, theprimary power conversion network 104 and the power factor correctiondevice 102. Likewise, as indicated by the curved arrow 1202, the poweris transferred from the DC power source 124 to the DC load 122 throughthe second network 142, the first network 141 and the secondary powerconversion network 112.

Referring back to FIG. 4 , the second network 142 is configured as aboost DC/DC converter. The first network 141 functions as a full-bridgeconverter converting the DC voltage generated by the boost DC/DCconverter into an alternating polarity waveform. The alternatingpolarity waveform is fed into the primary power conversion network 104through the magnetic coupling between NS2 and NP. The primary powerconversion network 104 functions as a rectifier converting thealternating polarity waveform into a single polarity waveform. The powerfactor correction device 102 is configured as an inverter, through whichthe single polarity waveform is converted into an AC waveform, which isapplied to the AC load 101. Furthermore, the alternating polaritywaveform generated by the first network 141 is fed into the secondarypower conversion network 112 through the magnetic coupling between NS2and NS11/NS12. The secondary power conversion network 112 functions as arectifier converting the alternating polarity waveform into a singlepolarity waveform. The single polarity waveform is a DC voltage, whichis applied to the DC load 122.

FIG. 13 illustrates a block diagram of the bidirectional three-portpower conversion system after both the first DC load and the second DCload of the bidirectional three-port power conversion system areconfigured as power sources to provide power for an AC load inaccordance with various embodiments of the present disclosure. In someembodiments, the AC power source may be disconnected from thebidirectional three-port power conversion system 200. The AC element 101is implemented as an AC load. Both the DC element 122 and DC element 124are batteries, which have been fully charged.

In response to this system configuration change, both the DC element 122and the DC element 124 may be configured as DC power sources. Asindicated by the curved arrows 1302 and 1304, the power is transferredfrom the DC power sources 122 and 124 to the AC load 101. The powertransferring path from the DC power source 122 to the AC load 101 hasbeen described above with respect to FIG. 8 , and hence is not discussedagain herein. Likewise, the power transferring path from the DC powersource 124 to the AC load 101 has been described above with respect toFIG. 11 , and hence is not discussed again herein. In some embodiments,the DC power sources 122 and 124 may transfer power to the AC load 101simultaneously. In alternative embodiments, the DC power sources 122 and124 may transfer power to the AC load 101 in an alternating manner.

FIG. 14 illustrates a flow chart of a method for controlling thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure. Thisflowchart shown in FIG. 14 is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,various steps illustrated in FIG. 14 may be added, removed, replaced,rearranged and repeated.

A bidirectional three-port power conversion system comprises a powerfactor correction device and an isolated power converter having threeports. A first port is connected to the power factor correction devicethrough a primary power conversion network. The primary power conversionnetwork may be implemented as a three-level LLC power converter. Asecond port is connected to a first DC load through a secondary powerconverter network. The secondary power converter network functions as arectifier. A third port is connected to a second DC load through a firstnetwork and a second network. The first network is implemented as arectifier. The second network is implemented as a power regulator suchas a buck DC/DC converter.

In operation, the voltage applied to the first DC load is regulatedmainly through adjusting the output voltage of the power factorcorrection device in a wide range and partially through adjusting theswitching frequency of the three-level LLC converter in a narrow range.It should be noted that the regulation of the LLC resonant converter maybe achieved through a variety of control methods such as PWM controlmechanisms, phase modulation control mechanisms and/or frequencymodulation control mechanisms. The control mechanisms of LLC resonantconverters above are well known in the art, and hence are not discussedin detail herein to avoid unnecessary repetition.

At step 1402, the three-port power conversion system is employed toconvert an AC voltage from a single-phase AC source into a first DCvoltage for a first DC load and a second DC voltage for a second DCload. In some embodiments, the first DC load is a main battery of anelectric vehicle. The second DC load is an auxiliary battery of theelectric vehicle. The primary side of the three-port power conversionsystem comprises a power factor correction device and an LLC resonantconverter. The first DC load is connected to the secondary side of thethree-port power conversion system through a first rectifier apparatus.The second DC load is connected to the secondary side of the three-portpower conversion system through a second rectifier apparatus and asecondary regulator. The secondary regulator is implemented as a buckDC/DC converter.

In operation, the first DC voltage is regulated mainly throughregulating the output voltage of the power factor correction device andpartially through adjusting the LLC resonant converter in a narrowrange. The second DC voltage is regulated through adjusting the dutycycle of the secondary regulator.

At step 1404, a suitable voltage sensor detects an input voltage fedinto the secondary regulator. A controller is employed to compare thedetected input voltage with a predetermined voltage range.

At step 1406, the secondary regulator is configured to operate in abypass mode when the input voltage applied to the secondary regulator iswithin the predetermined voltage range. In the bypass mode, thehigh-side switch of the secondary regulator is configured as analways-on switch. The low-side switch of the secondary regulator isconfigured as an always-off switch. One advantageous feature of havingthe bypass mode is the switching losses of the secondary regulator canbe saved, thereby improving the efficiency of the three-port powerconversion system.

FIG. 15 illustrates a flow chart of another method for controlling thebidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure. Thisflowchart shown in FIG. 15 is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,various steps illustrated in FIG. 15 may be added, removed, replaced,rearranged and repeated.

At step 1502, a three-port power conversion system is employed toconvert an AC voltage from a single-phase AC source into a first DCvoltage for a first DC load and a second DC voltage for a second DCload. In some embodiments, the first DC load is a main battery of anelectric vehicle. The second DC load is an auxiliary battery of theelectric vehicle. The primary side of the three-port power conversionsystem comprises a power factor correction device and an LLC resonantconverter. The first DC load is connected to the secondary side of thethree-port power conversion system through a first rectifier apparatus.The second DC load is connected to the secondary side of the three-portpower conversion system through a second rectifier apparatus and asecondary regulator. The secondary regulator is implemented as a buckDC/DC converter.

In operation, the first DC voltage is regulated mainly throughregulating the output voltage of the power factor correction device andpartially through adjusting the LLC resonant converter in a narrowrange. The second DC voltage is regulated through adjusting the dutycycle of the secondary regulator.

At step 1504, a suitable voltage sensor detects an input voltage fedinto the secondary regulator. A controller is employed to compare thedetected input voltage with a predetermined voltage range.

At step 1506, the secondary regulator is configured as a linearregulator when the input voltage applied to the secondary regulator iswithin the predetermined voltage range. As a linear regulator, theoutput voltage of the linear regulator is regulated through controllingthe voltage drop across the high-side switch of the secondary regulator.The low-side switch of the secondary regulator is configured as analways-off switch. One advantageous feature of configuring the secondaryregulator as a linear regulator is the secondary regulator is able togenerate a noise-free voltage suitable for DC loads sensitive to powersupply noise.

FIG. 16 illustrates a flow chart of yet another method for controllingthe bidirectional three-port power conversion system shown in FIG. 3 inaccordance with various embodiments of the present disclosure. Thisflowchart shown in FIG. 16 is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,various steps illustrated in FIG. 16 may be added, removed, replaced,rearranged and repeated.

Referring back to FIG. 4 , the three-level LLC resonant converter 104and the first network 141 may is configured to operate at a boostconverter mode. During the boost converter mode, the regulation of theoutput voltage of the LLC resonant converter is achieved through forcingthe LLC resonant converter to operate in a manner similar to a boostconverter. In particular, at the beginning of each switching period,switches S32 and S34 are simultaneously turned on and remain theon-state for a predetermined time period. Throughout the description,the predetermined time period is alternatively referred to as a boostperiod. During the boost period, switches S31 and S33 are turned off toprevent shoot-through.

During the boost period, the three-level LLC resonant converter 104 mayoperate in three different operating modes. In a first operating mode,during the boost period, switches S7 and S10 are in the on-state. Theturned-on switches S7 and S10 lead to a first positive voltage appliedto the input terminals of the resonant tank. At the same time, theturned-on switches S32 and S34 may short the secondary side winding ofthe transformer 191. Since the secondary side voltage of the transformer191 is approximately equal to zero during the boost period, thereflected voltage at the primary side of the transformer 191 isapproximately equal to zero. As a result, the input voltage is directlyapplied to the resonant tank. In response to such a voltage applied tothe resonant tank, the current flowing through the resonant inductor Lrramps up quickly in a manner similar to the current flowing through aboost inductor during the on period of a boost converter. In a secondoperating mode, during the boost period, switches S7 and S9 are in theon-state. The turned-on switches S7 and S9 lead to a second positivevoltage applied to the input terminals of the resonant tank. The secondpositive voltage is about one half of the first positive voltage.Similar to the first operating mode, in response to the second positivevoltage applied to the input terminals of the resonant tank, the currentflowing through the resonant inductor Lr ramps up quickly in a mannersimilar to the current flowing through a boost inductor during the onperiod of a boost converter. In a third operating mode, during the boostperiod, switches S8 and S10 are in the on-state. The turned-on switchesS8 and S10 lead to a third positive voltage applied to the inputterminals of the resonant tank. The third positive voltage is about onehalf of the first positive voltage. Similar to the first operating mode,in response to the third positive voltage applied to the input terminalsof the resonant tank, the current flowing through the resonant inductorLr ramps up quickly in a manner similar to the current flowing through aboost inductor during the on period of a boost converter.

The energy is accumulated in the resonant inductor Lr. During asubsequent time period, the accumulated energy is released to the outputof the LLC resonant converter. As a result, the output voltage of theLLC resonant converter is boosted to a higher level.

At step 1602, a three-port power conversion system is employed toconvert an AC voltage from a single-phase AC source into a first DCvoltage for a first DC load and a second DC voltage for a second DCload. In some embodiments, the first DC load is a main battery of anelectric vehicle. The second DC load is an auxiliary battery of theelectric vehicle. The primary side of the three-port power conversionsystem comprises a power factor correction device and an LLC resonantconverter. The first DC load is connected to the secondary side of thethree-port power conversion system through a first rectifier apparatus.The second DC load is connected to the secondary side of the three-portpower conversion system through a second rectifier apparatus and asecondary regulator. The secondary regulator is implemented as a buckDC/DC converter.

In operation, the first DC voltage is regulated mainly throughregulating the output voltage of the power factor correction device andpartially through adjusting the LLC resonant converter in a narrowrange. The second DC voltage is regulated through adjusting the dutycycle of the secondary regulator.

At step 1604, a suitable voltage sensor detects an input voltage fedinto the secondary regulator.

At step 1606, after the input voltage of the secondary regulator isbelow a predetermined voltage threshold, the low side switches of thesecond rectifier are turned on simultaneously so as to short thesecondary winding. As a result of having a shorted secondary winding,the output voltage of the second rectifier is able to generate a highervoltage.

Although embodiments of the present disclosure and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present disclosure, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present disclosure. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps. The specification anddrawings are, accordingly, to be regarded simply as an illustration ofthe disclosure as defined by the appended claims, and are contemplatedto cover any and all modifications, variations, combinations orequivalents that fall within the scope of the present disclosure.

What is claimed is:
 1. A method comprising: configuring a bidirectionalmultiple-port power conversion system as an alternating current(AC)/direct current (DC) power conversion system in response to an ACpower source coupled to an input of the bidirectional multiple-portpower conversion system, wherein a first port of the bidirectionalmultiple-port power conversion system comprises a power factorcorrection device and a primary power conversion network connected incascade between an input of the first port and a primary winding of atransformer, a second port of the bidirectional multiple-port powerconversion system comprises a plurality of switches and a plurality ofdiodes connected between a secondary side of the transformer and anoutput of the second port, and a third port of the bidirectionalmultiple-port power conversion system comprises a first switch networkand a power regulator connected in cascade between the secondary side ofthe transformer and an output of the third port; and configuring thebidirectional multiple-port power conversion system as a DC/DC powerconversion system in response to disconnecting the AC power source fromthe input of the bidirectional multiple-port power conversion system. 2.The method of claim 1, wherein the bidirectional multiple-port powerconversion system comprises three ports, and wherein: the input of thefirst port of the bidirectional multiple-port power conversion system isconfigured to be coupled to an AC element; the output of the second portof the bidirectional multiple-port power conversion system is configuredto be coupled to a first DC element; and the output of the third port ofthe bidirectional multiple-port power conversion system is configured tobe coupled to a second DC element.
 3. The method of claim 2, furthercomprising: configuring the first DC element as a DC power source; andconfiguring the second DC element as a DC load, wherein power istransferred from the DC power source to the DC load.
 4. The method ofclaim 2, further comprising: configuring the first DC element as a DCpower source; and configuring the AC element as an AC load, whereinpower is transferred from the DC power source to the AC load.
 5. Themethod of claim 2, further comprising: configuring the first DC elementas a DC power source; configuring the second DC element as a DC load;and configuring the AC element as an AC load, wherein the DC powersource is configured to provide power to the DC load and the AC loadsimultaneously.
 6. The method of claim 2, further comprising:configuring the first DC element as a DC power source; configuring theplurality of switches and the plurality of diodes as a full-bridgeswitching network; configuring the primary power conversion network as arectifier; configuring the power factor correction device as aninverter; and configuring the AC element as an AC load, wherein power istransferred from the DC power source to the AC load.
 7. The method ofclaim 1, wherein: the power factor correction device is a neutral-pointclamped boost power factor correction converter; and the primary powerconversion network is a three-level inductor-inductor-capacitor (LLC)resonant converter.
 8. The method of claim 1, wherein: the plurality ofswitches and the plurality of diodes form a first rectifier comprisingthree diodes and one switch, and a second rectifier comprising fourswitches.
 9. The method of claim 8, further comprising: configuring thefirst rectifier as a first voltage doubler and the second rectifier as asecond voltage doubler through configuring the one switch of the firstrectifier and one switch of the second rectifier as always-on switches.10. A method comprising: transferring energy in a bidirectionalmultiple-port power conversion system including a first port configuredto be coupled to an alternating current (AC) element, a second portconfigured to be coupled to a first direct current (DC) element, and athird port configured to be coupled to a second DC element, wherein: thefirst port comprises a power factor correction device and a primarypower conversion network connected in cascade between an input of thefirst port and a first winding of a transformer; the second portcomprises a secondary power conversion network comprising a first bridgeand a second bridge connected in parallel, and wherein the first bridgeis between a second winding of the transformer and the first DC element,and the second bridge is between a third winding of the transformer andthe first DC element; and the third port comprising a first network anda second network connected in cascade between a fourth winding of thetransformer and the second DC element; and configuring the bidirectionalmultiple-port power conversion system as an AC/DC power conversionsystem in response to an AC power source coupled to the first port, andconfiguring the bidirectional multiple-port power conversion system as aDC/DC power conversion system or a DC/AC power conversion system inresponse to disconnecting the AC power source from the first port. 11.The method of claim 10, further comprising: configuring the first DCelement as a DC power source; configuring the second DC element as a DCload; and transferring power from the DC power source to the DC loadthrough the secondary power conversion network, the first network andthe second network.
 12. The method of claim 10, further comprising:configuring the first DC element as a DC power source; configuring theAC element as an AC load; and transferring power from the DC powersource to the AC load through the secondary power conversion network,the primary power conversion network and the power factor correctiondevice.
 13. The method of claim 10, further comprising: configuring thesecond DC element as a DC power source; configuring the first DC elementas a DC load; and transferring power from the DC power source to the DCload through the second network, the first network and the secondarypower conversion network.
 14. The method of claim 10, furthercomprising: configuring the second DC element as a DC power source;configuring the AC element as an AC load; and transferring power fromthe DC power source to the AC load through the second network, the firstnetwork, the primary power conversion network and the power factorcorrection device.
 15. The method of claim 10, further comprising:configuring the first DC element as a first DC power source configuringthe second DC element as a second DC power source; configuring the ACelement as an AC load; transferring power from the first DC power sourceto the AC load through the secondary power conversion network, theprimary power conversion network and the power factor correction device;and transferring power from the second DC power source to the AC loadthrough the second network, the first network, the primary powerconversion network and the power factor correction device.